Governmental requirements for the onboard diagnostics (OBD) of engine misfires necessitate specialized instrumentation to develop, calibrate, and test misfire detection algorithms. Specifically, equipment designed to induce engine misfires at precisely controlled rates is needed to determine thresholds for emissions and signal detection, and to demonstrate regulatory compliance. This "misfire generator" must interact with the engine's ignition system so as to prevent spark for certain firing events, without affecting the normal firing events before and after each occurrence.